I Once gave a series of talks to a group of psychoanalysts who had trained together and was rather struck by the statement made by one of them that, psychologically speaking, ‘reason’ means saying ‘No’ to oneself. Plato, of course, introduced the concept of ‘reason’ in a similar way in The Republic with the case of the thirsty man who is checked in the satisfaction of his thirst by reflection on the outcome of drinking. But Plato was also so impressed by man's ability to construct mathematical systems by reasoning that he called it the divine element of the soul. And what has this ability to do with that of saying ‘No’ to oneself? And what have either of these abilities to do with the disposition to be impartial which is intimately connected with our notion of a reasonable man, or with what David Hume called a ‘wonderful and unintelligible instinct’ in our souls by means of which men are able to make inferences from past to future?

It must readily be admitted that there are few surface similarities between the uses of ‘reason’ in these contexts. No obvious features protrude which might be fastened on as logically necessary conditions for the use of the term ‘reason’. But beneath the surface there may be lurking common notions that are, or can be, of importance in our lives. To make them explicit is to give structure and substance to what is often called ‘the life of reason’ and to show that this is not inconsistent with a life of passion as is often thought. This seems eminently worth attempting at a time when many people seem hostile to reason. For those who demand instant gratification, who adopt some existentialist stance, who cultivate violence or mystical experience, or who merely do what others do, are all, in various ways, resisting the claims of reason on them. And what they are resisting is not just the demand that they should reflect and calculate; it is also the influence of passions and sentiments that underlie a form of life.